Band PAss filter at 70MHz
centre frequency : 70 MHz
pass band : 62-68 MHz
Rejection : 20dB@58 MHz, 20dB@72MHz
I have used air core inductor and silver mica capacitors. I am taking fifth order for designing it. When I am simulating it with ADS I am getting good results but when I am fabricating and testing with VNA then I am getting pass band more than what I have achieved in simulation. What could be the reason and how to make precise and accurate band pass filter at VHF using lumped element? Is there any good reference material for that?
Regards,
Hi
Maybee you are already doing it, but one thing you can/must do, is to use models for your inductors and capacitors. They can sometimes be found from vendors.
Regards
I think, the capacitors could be regarded ideal except for series inductance (that may be modelled with systematic value), but the inductor limited Q due to series resistance (DC and frequency dependant skin effect losses) reduces the filter Q and increases bandwith. A Q value at the filter frequency from the datasheet (could be converted into a series resistance) is usually sufficient for a realistic filter calculation. Additionally an inductor parallel capacitance could be calculated from self resonance datasheet values and used in the simulation.
But I have used air core inductor which I have made myself by coil winding so how to obtain Q of that? And other problem is that How can I tune the filter to improve return loss? How will I know which Inductor to squeeze or expand to improve the respone. Any help?
Have you taken into account parasitics of your layout? There are stray capacitance from the component connection pads to ground. And there is a stray inductance as well of component interconnections and wires, about 1 nH/mm.
Can you post a schematic diagram and a layout drawing of your design?
Whatsa "silver mica" capacitor? Something my grandpa used to listen to the ole fireside theatre?
Get with the program and use some chip ceramic, or if high power some porcelain caps.